The S/N (serial number) is the serial number of your device.
You can find it on the back of the packaging of your device or the back of your ZeCircle2.
The D/N (device number) is the device number associated to your account.
You can find it in the Settings menu of your ZeCircle2. Select to see it.
You can also find it in the Settings tab of the ZeCircle2 application. Then, click on the help section menu.
The D/N is associated with your email address. You must unpair your ZeCircle2 from your account through the app to connect your ZeCircle2 with another account.